The present invention relates generally to a solenoid operated exhaust gas recirculation valve, and more specifically, to a solenoid operated exhaust gas recirculation valve that is smaller than prior valves and eliminates any valve dithering.
Exhaust gas recirculation (xe2x80x9cEGRxe2x80x9d) valves form an integral part of the exhaust gas emissions control in typical internal combustion engines. EGR valves are utilized to recirculate a predetermined amount of exhaust gas back to the intake system of the engine. The amount of exhaust gas permitted to flow back to the intake system is usually controlled in an open-looped fashion by controlling the flow area of the valve, i.e., the amount of exhaust gas that is permitted to flow through the valve. Such open-loop control makes it difficult to accurately control the exhaust gas flow through the valve over the valve""s useful life. This is because the valve has various components that can wear. Moreover, vacuum signals which are communicated to such valves will vary or fluctuate over time resulting in the potential contamination of various valve components which could affect the operation of the valve.
Many EGR valves utilize a moveable diaphragm to open and close the valves. However, these valves can lack precision because of the loss of vacuum due to external leakpaths. To overcome the lack of consistently available vacuum to control a movable diaphragm, electrically actuated solenoids have been used to replace the vacuum actuated diaphragm. Moreover, typical vacuum actuated valves can also have problems with accuracy due to their inability to quickly respond based on changes in engine operating conditions. Further, current EGR valves typically have an inwardly opening valve closure element that is moved into its valve housing relative to a cooperating valve seat in order to open the valve. Over the useful life of these valves, carbon can accumulate on the valve closure element and upon its valve seat, thereby preventing the valve from completely closing. The valve closure elements are also positioned within the housing or body of these EGR valves and because it is virtually impossible to clean the valve closure element and the valve seat, contamination thereby necessitates replacement of these integral pollution system components.
Additionally, exhaust gas recirculation valves that require a high force to open the valve, operate through pressure balancing, whether through a diaphragm or other balancing members. Alternatively, too low a force can open the valve allowing exhaust gas to flow through the valve opening when such exhaust gas is not needed. By allowing exhaust gas to act as part of the pressure balance, it necessarily contacts the internal moving parts of the valve causing contaminants to accumulate thereon which can interfere with the proper operation of the valve, as discussed above.
As is known, in these current solenoid actuated EGR valves, flux travels through a path from the flux washer through the armature and then through the pole piece. The configuration of this magnetic circuit works effectively to control movement of the armature and thus the location of the valve in the valve seat. However, in the desire to produce smaller valves, engine pulses can cause dithering, i.e. movement of the valve with respect to the valve seat. This can cause inefficiencies as well as other problems.
Therefore, a need arises for a smaller EGR valve that minimizes any valve dithering.
It is, therefore, an object of the present invention to provide an improved electromechanically actuated EGR valve that is used to meter and control the passage of exhaust gases from an exhaust passage to the intake system of an internal combustion engine.
It is another object of the present invention to provide an electromechanically actuated EGR valve that helps reduce an engine""s emissions of environmentally unfriendly elements.
It is a further object of the present invention to provide a solenoid operated EGR valve that minimizes valve dithering.
It is still a further object of the present invention to provide a solenoid operated EGR valve that induces electromagnetic damping.
In accordance with the above and other objects of the present invention, a solenoid actuated EGR valve for an engine is disclosed. The EGR valve includes a valve housing and a motor housing. The valve housing includes a valve inlet adapted to receive exhaust gas and a valve outlet adapted to communicate the received exhaust gas to an intake manifold of the engine. The motor housing is positioned above the valve housing and has an electromagnetic mechanism disposed therein, which includes a plurality of wire windings, a bobbin, an armature, and a valve stem in communication with the armature. The armature is moved due to increased current that creates electromagnetic forces created in the magnetic circuit which moves the valve stem with respect to a valve seat that is located in the valve housing around the periphery of a valve opening. A plunger extends from a sensor housing positioned above the motor housing to monitor the position of the valve stem. A guide bearing is disposed within the motor housing and is in communication with the armature to help position the armature concentrically within the magnetic circuit. The guide bearing is in communication at an upper portion with a flux washer and at a lower portion with a pole piece. The guide bearing is sized so that any radial air gap between the flux washer and the pole piece is reduced to cause at least some amount of shorting therebetween.
These and other features and advantages of the present invention will become apparent from the following descriptions of the invention, when viewed in accordance with the accompanying drawings and appended claims.